1. Field of the Invention:
This invention relates to joinder of plastic elements, such as plastic conduit. More particularly, this invention relates to the elements of plastic conduit, such as conduit sections and fittings; and to the apparatus and method for joining the elements into a desired distribution network, as for liquids like water; gases like steam and semi-solids like slurries.
2. Description of the Prior Art:
The prior art has seen a wide variety of thermoplastic elements and their joinder. The joinder of the thermoplastic elements has involved, heretofore, the use of solvents or the melting of one or both of the pieces of plastic and the immobilization of the pieces of plastic in the desired relationship to each other for fusion of the elements. Where plastic conduit was desired to be joined in fluid tight relationship, this has taken the form of heating of tubular ends and socket ends, joinder thereof, and immobilization in a jig or the like for 20-90 seconds while awaiting for the fusion to take place. There was a tendency to cause a notching, or necking down, and stress cracking, of the conduit walls near the fitting. If, in the interim, there was relative movement between the contiguous surfaces, a leak was effected, resulting in a relatively high percentage of imperfect seals. Moreover, metal stiffeners in small diameter pipe, have to be longer than the fitting socket to support the weakened and thinned conduit, which often cause destruction in that the stiffeners themselves cause notching of conduit thereby creating stress and leaks. Typically, commercial installations have required as much as six to ten percent of the joints formed to be cut out of a given job. This is a very expensive and time consuming process. Also the time of holding the elements in a jig or the like has slowed down production and caused appreciable expense.
My experience in this art over several years has indicated that a method of joining thermoplastic elements, such as pipe and fittings, should have the following desirable features not heretofore provided:
1. The conduit, fittings, apparatus and method should not require an internal stiffener that has frequently cut the conduit heretofore.
2. The conduit walls should not be thinned, as was done by notching, or drawing, of the conduit walls in the prior art. Consequently, the prior art pipe has had a low strength whereas it is desirable that the conduit have a greater strength adjacent the fitting than heretofore provided.
3. It is desirable that there be a substantially immediate physical fixation to eliminate the requirement for immobilization for a protracted interval of time as has been required in the prior art; yet, the method of joinder should provide a sealing fusion of hot-to-hot plastic.
4. The method should eliminate the streaming of the molten plastic back alongside tubular ends of conduit inserted within the fittings with the attendant leaks, as has frequently occurred in the prior art.
5. It is desirable that the method provide a strong joint, that cannot be pulled apart by providing at least an annular lip that engages an annular recess, or groove.
6. It is desirable that the method not only eliminate the need for protracted holding, but eliminate the relatively high percentage of inferior joints of the prior art because of relative movement between the fusing parts during the fusion process.